Various proposals have been made heretofore for strain insulators equipped with arcing horns to protect a high tension line and the insulator itself if a flashover occurs across the insulator. Such flashovers can arise from numerous causes including abnormal operating conditions on the line, a lightning strike, damage to the insulator caused by impact with foreign objects, and the collection of a coating on the insulator due to environmental conditions. Serious results can follow unless the insulator is provided with a protective device such as an arcing horn. Typically, such horns comprise an accessory clampable to the insulator or to its terminal hardware and disposed to provide a conductive path for the arc suitably spaced from the surface of the insulator. The proper functioning of such horns is dependent on the care with which they are secured to the insulators and adjusted to provide a desired arcing gap. The gap adjustment may be disturbed during installation or may be improperly made at the time of installation. The mounting devices add to the cost of the insulator assembly and this is further increased by the charge involved in adjusting and setting the arcing gap. A further and important shortcoming of prior insulators equipped with arcing horns is their lack of versatility to meet the needs of differing operating environments and their disposition relative to horizontal and vertical planes. It is important that the horns diverge upwardly away from a horizontal plane so as to be automatically self-extinguishing. This need is easily satisfied if the insulator axis is generally horizontal; however this need may not be satisfied if the insulator is installed sharply inclined to the horizontal.